#region Copyright notice and license

// Copyright 2018 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#endregion

using System;
using System.Linq;
using Grpc.Core.Utils;

namespace Grpc.Core.Interceptors;

/// <summary>
/// Extends the CallInvoker class to provide the interceptor facility on the client side.
/// </summary>
public static class CallInvokerExtensions
{
    /// <summary>
    /// Returns a <see cref="Grpc.Core.CallInvoker" /> instance that intercepts
    /// the invoker with the given interceptor.
    /// </summary>
    /// <param name="invoker">The underlying invoker to intercept.</param>
    /// <param name="interceptor">The interceptor to intercept calls to the invoker with.</param>
    /// <remarks>
    /// Multiple interceptors can be added on top of each other by calling
    /// "invoker.Intercept(a, b, c)".  The order of invocation will be "a", "b", and then "c".
    /// Interceptors can be later added to an existing intercepted CallInvoker, effectively
    /// building a chain like "invoker.Intercept(c).Intercept(b).Intercept(a)".  Note that
    /// in this case, the last interceptor added will be the first to take control.
    /// </remarks>
    public static CallInvoker Intercept(this CallInvoker invoker, Interceptor interceptor)
    {
        return new InterceptingCallInvoker(invoker, interceptor);
    }

    /// <summary>
    /// Returns a <see cref="Grpc.Core.CallInvoker" /> instance that intercepts
    /// the invoker with the given interceptors.
    /// </summary>
    /// <param name="invoker">The channel to intercept.</param>
    /// <param name="interceptors">
    /// An array of interceptors to intercept the calls to the invoker with.
    /// Control is passed to the interceptors in the order specified.
    /// </param>
    /// <remarks>
    /// Multiple interceptors can be added on top of each other by calling
    /// "invoker.Intercept(a, b, c)".  The order of invocation will be "a", "b", and then "c".
    /// Interceptors can be later added to an existing intercepted CallInvoker, effectively
    /// building a chain like "invoker.Intercept(c).Intercept(b).Intercept(a)".  Note that
    /// in this case, the last interceptor added will be the first to take control.
    /// </remarks>
    public static CallInvoker Intercept(this CallInvoker invoker, params Interceptor[] interceptors)
    {
        GrpcPreconditions.CheckNotNull(invoker, nameof(invoker));
        GrpcPreconditions.CheckNotNull(interceptors, nameof(interceptors));

        foreach (var interceptor in interceptors.Reverse())
        {
            invoker = Intercept(invoker, interceptor);
        }

        return invoker;
    }

    /// <summary>
    /// Returns a <see cref="Grpc.Core.CallInvoker" /> instance that intercepts
    /// the invoker with the given interceptor.
    /// </summary>
    /// <param name="invoker">The underlying invoker to intercept.</param>
    /// <param name="interceptor">
    /// An interceptor delegate that takes the request metadata to be sent with an outgoing call
    /// and returns a <see cref="Grpc.Core.Metadata" /> instance that will replace the existing
    /// invocation metadata.
    /// </param>
    /// <remarks>
    /// Multiple interceptors can be added on top of each other by
    /// building a chain like "invoker.Intercept(c).Intercept(b).Intercept(a)".  Note that
    /// in this case, the last interceptor added will be the first to take control.
    /// </remarks>
    public static CallInvoker Intercept(this CallInvoker invoker, Func<Metadata, Metadata> interceptor)
    {
        return new InterceptingCallInvoker(invoker, new MetadataInterceptor(interceptor));
    }

    private class MetadataInterceptor : Interceptor
    {
        readonly Func<Metadata, Metadata> interceptor;

        /// <summary>
        /// Creates a new instance of MetadataInterceptor given the specified interceptor function.
        /// </summary>
        public MetadataInterceptor(Func<Metadata, Metadata> interceptor)
        {
            this.interceptor = GrpcPreconditions.CheckNotNull(interceptor, nameof(interceptor));
        }

        private ClientInterceptorContext<TRequest, TResponse> GetNewContext<TRequest, TResponse>(ClientInterceptorContext<TRequest, TResponse> context)
            where TRequest : class
            where TResponse : class
        {
            var metadata = context.Options.Headers ?? new Metadata();
            return new ClientInterceptorContext<TRequest, TResponse>(context.Method, context.Host, context.Options.WithHeaders(interceptor(metadata)));
        }

        public override TResponse BlockingUnaryCall<TRequest, TResponse>(TRequest request, ClientInterceptorContext<TRequest, TResponse> context, BlockingUnaryCallContinuation<TRequest, TResponse> continuation)
        {
            return continuation(request, GetNewContext(context));
        }

        public override AsyncUnaryCall<TResponse> AsyncUnaryCall<TRequest, TResponse>(TRequest request, ClientInterceptorContext<TRequest, TResponse> context, AsyncUnaryCallContinuation<TRequest, TResponse> continuation)
        {
            return continuation(request, GetNewContext(context));
        }

        public override AsyncServerStreamingCall<TResponse> AsyncServerStreamingCall<TRequest, TResponse>(TRequest request, ClientInterceptorContext<TRequest, TResponse> context, AsyncServerStreamingCallContinuation<TRequest, TResponse> continuation)
        {
            return continuation(request, GetNewContext(context));
        }

        public override AsyncClientStreamingCall<TRequest, TResponse> AsyncClientStreamingCall<TRequest, TResponse>(ClientInterceptorContext<TRequest, TResponse> context, AsyncClientStreamingCallContinuation<TRequest, TResponse> continuation)
        {
            return continuation(GetNewContext(context));
        }

        public override AsyncDuplexStreamingCall<TRequest, TResponse> AsyncDuplexStreamingCall<TRequest, TResponse>(ClientInterceptorContext<TRequest, TResponse> context, AsyncDuplexStreamingCallContinuation<TRequest, TResponse> continuation)
        {
            return continuation(GetNewContext(context));
        }
    }
}
